Abstract: Three experiments examined whether negative priming is a dually determined effect produced by inhibitory mechanisms and by a memorial process. Younger adults (Experiment 1) and older adults (Experiments 1-3) were tested in procedures that varied the likelihood of inducing retrieval of the prior trial. 'This was done by making test-trial target decoding difficult (Experiments 1 & 2) or by making prior information useful on some nonnegative priming trials (Experiment 3). Younger adults demonstrated negative priming under retrieval and nonretrieval conditions, with patterns of performance indicating different sources of negative priming effects. Older adults showed negative priming only under retrieval-inducing conditions, consistent with the view of deficient inhibitory mechanisms for older adults. The data suggest that contextual variables critically determine whether negative priming is largely due to inhibition or to episodic retrieval.